This invention relates in general to monitoring air brake systems for maintenance and operating safety and in particular to air brake systems found on heavy and medium trucks and buses.
In 1988, over 6,000 deaths, 160,000 injuries and countless millions of dollars in related expenses were attributed to motor carrier crashes involving heavy and medium truck and bus accidents (The Private Carrier, June 1990, pg. 13). "Out-of-adjustment brakes continue to be the number one defect in vehicle safety inspections. Fleets and owner-drivers either don't know how often brakes need adjustment, or aren't checking often enough" (Heavy Duty Trucking, November 1990, pg. 104).
Due to the absence of brake travel indicating devices, maintenance people, operators and all such involved persons must spend excess hours and manpower, often under inclement conditions, performing time-consuming and sometimes unnecessary brake maintenance procedures, procedures and manpower that could be more efficiently utilized with the use of a truly functional, durable and practical brake travel indicating system. Such a system would yield not only a more efficient cost-effective use of maintenance resources but would provide a greater margin of operating safety especially when necessary brake maintenance adjustments are neglected. Individual operators have no convenient way of knowing the braking capability of such vehicles and would also greatly benefit from readily available information discovered by a functional, durable, and practical brake travel indicating system that would provide an electrically supervised remote indicating display device as well as a local mechanical display device at the brake site. Some examples of prior art brake wear indicators are set forth in patents briefly described below:
U.S. Pat. No. 4,279,214 issued to Thorn discloses a loosely fitting sleeve with external indicia that installs over the pneumatic actuator pushrod of an air brake assembly and is frictionally engaged in the actuator housing push rod aperture Upon application of brakes, an internal diaphragm moving forward pushes the indicator outward exposing indicia that corresponds to push rod travel. The Thorn device is not easily observable at a distance and in some cases, not at all due to the actuator being awkwardly positioned and accumulation of road grime. No provision is made for remote indication capabilities.
U.S. Pat. Nos. 4,583,071 and 4,757,300 issued to Sebalos provide magnet and reed switch combinations where the magnet is adjustably secured to the pneumatic actuator pushrod of an air brake assembly which, when extended, will by magnetic flux operate a correspondingly mounted reed switch. The Sebalos devices make no provision for a locally displayed warning indicator and rely entirely upon electrically operated warning displays. A broken wire or power failure would render the systems inoperative and could promote a false sense of security by failing to annunciate an overtravel condition.
U.S. Pat. No. 4,642,603 issued to Martinez provides for an array of various contacts and spring mechanisms that are internal to the pneumatic actuator housing of an air brake assembly so that forward movement of the internal diaphragm closes corresponding contacts in turn lighting indicator lamps. Retrofitting existing actuators with this invention would be extremely difficult. The contacts are exposed to the severe elements of weather making them unreliable due to contact fouling from corrosion and road grime. No local mechanical display is provided. Fouled contacts and/or broken conductors would prevent overtravel warning leaving the operator with a false sense of security.
U.S. Pat. No. 4,776,438 issued to Schandelmeirer provides an adjustably locatable pointer suspended forwardly by a slotted bracket arrangement providing a stationary reference point against which the center line of a clevis pin of an air brake assembly may be referenced to determine overtravel. Reading accuracy would be compromised at different angles, brakes must be energized to read overtravel and no remote signaling means is provided.
U.S. Pat. No. 4,800,991 issued to Miller provides for an adjustable sliding aperture attached to the pushrod of an air brake assembly that cradles a pivotable springloaded telescoping flag arrangement that indicates only when overtravel occurs. Through independent switching means a remote signal can be provided. Failure of the switch or an open circuit would disable remote indication capabilities leaving the operator with a false sense of security. Confusion could occur due to nonsynchronization of electrical and mechanical detection means. Springs associated with the telescoping flag arrangement are prone to fatigue and breakage rendering the system unreliable. The sliding aperture requires access to an exposed portion of the pushrod for attachment. In many short-stroke actuators the exposed portion is not available making attachment impractical. No provision is made for universal adaptation to the various schemes of air brake mounting arrangements. The biasing spring of the system greatly increases the wear factor at tip of the flag and hole of the aperture reducing service life.
U.S. Pat. No. 4,879,964 issued to Emerson provides an adjustment marker secured to the pushrod of an air brake assembly comprising a round ball chain of a predetermined length with a snap at one end and a clamp at the other. Attached near the snap end is an indicator flag. With the clamp end attached to the brake actuator pushrod and the pushrod in an over-extended position, the snap releases dropping the flag downwardly. No provision is made to remotely indicate brake overtravel condition. The chain is susceptible to premature release due to impact from road debris, rocks, excessive icing and vibration. The clamp arrangement requires access to an exposed portion of the pushrod that is not available on many short-stroke brake actuators.
Whatever the precise merits, features and advantages of the aforecited references, none fulfills the purposes of the present invention.
Therefore, the principal object of the present invention is to reliably monitor and deliver critical brake overtravel information in such a way so as to provoke operating and/or maintenance personnel to perform corrective maintenance procedures on air brake systems primarily for heavy and medium trucks and buses.
Another principal object of the present invention is to provide dual brake travel indicating devices that operate dependently and reliably in a master/slave configuration.
A further object of the present invention is to provide multiple indicators that are easily and conveniently observed to encourage an operator to regularly inspect said devices and brakes.
Still another object of the present invention is to achieve a greater margin of operating safety for both driver and equipment hence enhancing the general public safety.
A further object of the present invention is to render said devices easily and universally installable and maintainable on all applicable vehicles by non-technical personnel.
Another object of the present invention is to enhance long service life due to materials and designs incorporated into this invention.
A further object of the present invention is to provide a method of quickly testing for brake overtravel from a remote location, i.e.: the front of a trailer, with a portable handheld test unit.
An additional object of the present invention is to provide electrical supervision of the monitoring circuit to enhance overall safety performance by detecting trouble such as broken wires, loss of power, poor connections, etc. and displaying such.
In general, on many vehicles utilizing brake systems with a plurality of pneumatic actuators comprising an elongated pushrod connected to a motion translating device such as a slack adjuster, linear motion directly proportional to the overall movement of the brake system can be monitored at the centerline of the clevis pin used to connect the elongated pushrod to the motion translating device. By elongating the non-head end of the clevis pin and slidingly placing a bored hole adapter plate over the extended portion of the elongated clevis pin, and by connecting the tang of the adapter plate to the internal diameter of a travel indicator tube, the free end of the travel indicator tube being slidingly suspended in an adjustable fixed reference tube and the fixed reference tube being adjustably attached to a universal extension bracket or existing mounting bracket, a unique means of monitoring overall brake travel is accomplished. When movement exceeds a predetermined limit as set by the length and placement of the fixed reference tube, the free end of the travel indicator tube pivots downwardly about its adapter end. In this freeswinging downward position, the travel indicator tube can be viewed from different angles and understood to represent an overtravel condition. Simultaneously, upon deployment of the travel indicator tube, an electrical monitoring system comprising a continuous electrical circuit with wiring, of environmentally tight multi-conductor cabling, connecting means, a switch means and sensing means, an intermediate junction box, remote display panel, power source, and over-current means operates to indicate a change in brake travel status on a remote indicating panel that in turn can be observed by an operator
Additionally a maintenance person can sub-feed a non-powered vehicle's electrical system with a portable power source and by observing the remote indicating panel, can ascertain brake travel status. This unique maintenance method can be used to quickly inspect any number of parked and/or non-powered vehicles.